Epidermoid cysts are an unusual form of brain tumour. Strictly speaking, they are not a tumour but rather an abnormality caused by the inclusion of skin cells within the brain cavity during brain formation.
How do they develop?
This condition effectively arises whilst being formed in the womb, but it is not in any way an inheritable or genetic condition. The skin cells themselves are not a problem, but over many years gradually produce keratin, which is the normal lining of the skin. This keratin accumulates and can start to put pressure on the adjacent brain during adult life. The size of the cyst is a function of the amount of skin cells and this means that they can present at any age from 20 to 60.
How do epidermoid cysts present?
The presenting features are varied and can be due to the irritant nature of the keratin or to the size of the cyst and pressure on the brain. The features with which the cyst can present include facial weakness or hemifacial spasm, trigeminal neuralgia and/or unsteadiness. Occasionally, they are picked up as an incidental finding on an MR scan done for other reasons.
Should an epidermoid cyst be treated?
The management of your epidermoid cyst will not only be discussed between you and your surgeon, but also at a Skull Base Multidisciplinary Team (MDT) Meeting. These are held fortnightly at Salford Royal Hospital, with a team of experts with a huge combined experience of managing such problems. Your surgeon will convey the outcome and recommendations of this meeting to you. Whilst this will provide you with all the information you require about your epidermoid cyst, as well as a detailed analysis of the advantages and disadvantages of all management options, the most important factor in the final decision is you. Your personal opinion of what is best for you is undoubtedly the most relevant aspect of how you will be managed.
How is an epidermoid cyst treated?
If treatment is required, this will be with surgery. The precise nature of the surgery and specifically its location will depend on the location of the epidermoid. In principle, the surgical philosophy is to make a craniotomy (opening of the head) in the best place to allow straightforward and safe access to the epidermoid. The epidermoid is then removed and the relatively soft nature of these tumours means that this is usually achieved in a relatively straightforward manner. However, the nature of an epidermoid is that the contents are contained within a very fine capsule (which contains the skin cells that formed the cyst). It is usually not possible to completely remove the capsule as it will be adherent to the brain and attempts to do so may cause harm.
Surgery is therefore aimed at removing the mass effect (related to the tumour volume) and thereby relieving any symptoms that he cyst was causing. The fine capsule is likely to remain to a greater or lesser extent, and this means there will be a chance of the cyst gradually recurring. We advise intermittent scans are carried out in the years following your surgery to monitor for any such re-growth of the epidermoid.
What are the risks of surgery?
Risks from surgery to epidermoid cysts fall into two categories:
- Risk to important adjacent structures. The risk of neurological harm from the surgery relates to the position of the tumour. A typical position of an epidermoid cyst might be near the facial, hearing and sensory nerves. In such a situation, the risk of the surgery would include the risk of post-operative deafness, numbness and facial weakness. The expertise and experience that we have with surgery means that such problems are extremely rare.
- Risk from the irritant nature of the contents of an epidermoid. This irritant quality means that there is a risk of post-operative inflammation of the meninges producing a chemical meningitis. Most people are familiar with meningitis as an infective process, whereas in this case the inflammation of the meninges is due to the irritant nature of the cyst contents. There are various techniques employed by your surgeon peri-operatively to minimise this risk but the consequences of a chemical meningitis can include hydrocephalus, which is a build-up of the cerebrospinal fluid (CSF).
The surgeons of the Brain and Spine Clinic have developed a range of techniques to minimise the risk of complications peri-operatively. They have recently re-audited their results to confirm that the risks are indeed very low. This work was presented in a paper entitled "Posterior fossa epidermoid cysts - keeping uncomplicated surgery uncomplicated" at the British Skull Base Society Meeting in Dublin in January 2015.